Audio experts' testimony at George Zimmerman's trial up in air

George Zimmerman, who has claimed self-defense and pleaded not guilty to second-degree murder in the death of Trayvon Martin, arrives at court Thursday in Sanford. Jury selection is to begin Monday.

SANFORD — An FBI voice examiner who tried to identify who was screaming in the background of a 911 call seconds before Trayvon Martin was shot testified Thursday that it couldn't be determined by a respectable scientist.

Hirotaka Nakasone testified that he dissected the 45-second sample and found only three seconds in which the screams were not at least partially obscured by other sounds. That's too little for a proper analysis, he said.

"It's not really feasible and not possible," he said, adding he was "disturbed" that other scientists made identifications anyway.

Some of those other scientists are scheduled to testify today at the continuation of a hearing that will determine whether Circuit Judge Debra S. Nelson lets jurors hear anyone's opinions about who made those cries for help.

Three audio experts have concluded that they either came from Martin, the unarmed 17-year-old who Zimmerman shot last year in Sanford, or ruled out Zimmerman.

Zimmerman, a former Neighborhood Watch volunteer, says it was him screaming after Martin had attacked him.

Zimmerman has pleaded not guilty to second-degree murder, claiming self-defense.

Earlier Thursday, the judge quickly rejected the request of three unidentified defense witnesses who had hired an attorney to ask that they testify from behind a screen and that their identities and names be kept secret.

They and three or four other witnesses are afraid that if Zimmerman is acquitted they'll face ridicule or worse, said defense attorney Mark O'Mara.

Attorneys for the Orlando Sentinel and more than a dozen other news organizations objected.

Defense attorneys also on Thursday filed paperwork asking the judge to ban from the trial anyone wearing a T-shirt or anything else as a sign of support for Martin or Zimmerman.